Shell and Tube Heat Exchanger | ASME Certified | Stainless Steel
What is shell and tube heat exchanger (STHE)?
A shell and tube heat exchanger (STHE) is the most widely used type
of heat exchanger in industrial applications due to its robustness,
versatility, and ability to handle high pressures and temperatures.
It consists of a shell (a large pressure vessel) with a bundle of
tubes inside. One fluid flows through the tubes (tube side), and
the other flows outside the tubes within the shell (shell side).
Heat is transferred between the two fluids through the tube walls.
STHEs are governed by two key standards:
1.ASME Boiler and Pressure Vessel Code (BPVC), Section VIII,
Division 1: Ensures pressure vessel safety.
2.TEMA (Tubular Exchanger Manufacturers Association) Standards:
Defines mechanical design, tolerances, and fabrication practices.
Key Technical Details as per ASME and TEMA
1.Design Standards
ASME BPVC Section VIII, Div. 1:
-Covers pressure boundary design (shell, tubesheets, channels).
-Requires calculations for minimum thickness, nozzle reinforcement,
and hydrostatic testing.
TEMA Standards (Classes R, C, B):
-Class R: Severe refinery and process applications (high
pressures/temperatures).
-Class C: General commercial/industrial service.
-Class B: Chemical process service (corrosive environments).
2. Components & Configuration
| Component | Description |
| Shell | Cylindrical vessel (carbon steel, stainless steel, etc.) per ASME
VIII-1. |
| Tubes | Straight/U-shaped tubes (OD 5/8" to 2"), material selected for
corrosion/thermal resistance. |
| Tubesheet | Thick plate drilled for tubes; designed per ASME VIII-1 (ligament
efficiency ≥ 50%). |
| Baffles | Segmental, helical, or rod-type baffles to direct shell-side flow
(TEMA spacing rules). |
| Channel/Header | Removable covers (TEMA front/rear head types: A, B, N, etc.). |
| Nozzles | Inlet/outlet ports sized per ASME B31.3 or API 660. |
TEMA Designation Example:
AES:
-A: Front head (bolted cover).
-E: One-pass shell.
-S: Floating rear head (pull-through bundle).
3. Thermal Design
Heat Duty (Q):Q=U⋅A⋅ΔTLMTD
-U: Overall heat transfer coefficient (W/m²·K).
-A: Heat transfer area (tube OD × length × number of tubes).
-ΔTLMTD: Log Mean Temperature Difference (corrected for flow arrangement).
Flow Arrangements:
-Counterflow: Highest thermal efficiency.
-Parallel Flow: Simpler but lower efficiency.
-Crossflow: Common in condensers.
Effectiveness-NTU Method:
-Used for complex flow arrangements or variable fluid properties.
4. Mechanical Design
Shell & Tube Dimensions:
-Shell ID: Determined by tube bundle layout (triangular, square,
rotated square).
-Tube pitch: Minimum 1.25 × tube OD (to allow cleaning).
Baffle Design:
-Segmental baffles (20–50% cut) with spacing per TEMA (min 1/5
shell ID or 2").
-No-Tubes-In-Window (NTIW): Eliminates dead zones.
Pressure Drop:
-Shell side: Optimized via baffle spacing/cut.
-Tube side: Function of fluid velocity and tube length.
5. Material Selection
| Component | Common Materials | ASME/TEMA Guidance |
| Shell | Carbon steel (SA-516), SS 316, Hastelloy | Corrosion allowance (3 mm typical). |
| Tubes | SS 304/316, Titanium, Cu-Ni, Inconel | Compatible with shell material to avoid galvanic corrosion. |
| Tubesheet | Clad materials (carbon steel + SS layer) | ASME VIII-1 for clad bonding requirements. |
| Gaskets | Spiral-wound (SS + graphite), PTFE | TEMA Class R/C/B for temperature/pressure limits. |
6. ASME Compliance & Testing
Hydrostatic Test:
-1.5 × design pressure (ASME VIII-1 UG-99).
-Test both shell and tube sides separately.
Pneumatic Test:
-1.1 × design pressure (if hydrostatic testing is impractical).
NDT Requirements:
-RT (radiographic testing) for welds.
-PT (dye penetrant) or MT (magnetic particle) for surface cracks.
7. Common Applications
Oil & Gas: Preheaters, coolers, condensers.
Power Plants: Steam condensers, feedwater heaters.
Chemical Industry: Reactor cooling, distillation.
HVAC: Chillers, district heating.
Advantages & Limitations
| Advantages | Limitations |
| High-pressure capability (ASME compliant). | Prone to fouling (shell side). |
| Easy to clean (removable tube bundles). | Larger footprint vs. plate heat exchangers. |
| Customizable (TEMA configurations). | Higher cost for exotic materials (Titanium). |
